Field of the Invention
This invention relates to a process for producing antimony trioxide having a low alpha-ray strength.
It has recently been discovered that highly integrate circuits which are packaged in materials which emit alpha rays can become damaged by these alpha rays. In fact, they can become so damaged that they will not operate properly. Materials which are normally used to package highly integrate circuits and which emit alpha rays include metals, ceramics and plastics. Plastics such as epoxy resins are most often used because they are the least expensive.
With regard to the foregoing, because the plastic materials which are used to package the highly integrated circuits must be resistant to fire, they usually include antimony trioxide, which is a flame retardant substance.
The antimony trioxide which is used for this purpose usually has an alpha-ray strength of, say, 0.1 to 0.5 C (counts)/cm.sup.2 per hour. In the event that antimony trioxide is added to the plastic used for packaging a highly integrated circuit, it is necessary to reduce its alpha-ray strength to a level not exceeding 0.1 C/cm.sup.2 per hour. Further reductions will undoubtedly be desired in the future.
Such antimony trioxide has hitherto been produced by melting and oxidizing antimony sulfide ores at a temperature of 900.degree. C. to 1000.degree. C., as disclosed, for example, in French Pat. No. 428,708, issued on Sept. 6, 1911. This method, however, fails to completely remove elements causing alpha-decay, such as uranium or thorium, which exist in a very small quantity in the ores. Those elements remain responsible for the emission of alpha rays by antimony trioxide.